1. Field of the Invention
The present invention relates to a method of manufacturing a polycrystalline silicon thin film.
2. Description of the Related Art
Conventionally, for manufacturing, for example, a thin film transistor by converting an amorphous silicon thin film into a polycrystalline silicon thin film, there is proposed a method in which an amorphous silicon thin film is formed on an entire surface of an insulating substrate such as a glass substrate having relatively a large size, an eximer laser beam is radiated on the amorphous silicon thin film so as to convert the amorphous silicon thin film into a polycrystalline silicon thin film, and the polycrystalline silicon thin film is separated into elements, thus manufacturing a number of thin film transistors. In this method, the eximer laser beam is scanned in order to radiate the beam on the entire amorphous silicon thin film on the insulating substrate, since the beam size of the eximer laser beam is as small as about 10 mm square at maximum, as compared with the size of the insulating substrate.
In the above-described conventional method of manufacturing a polycrystalline silicon thin film, the radiation of beams must be overlaped in the boundary sections between regions irradiated with a laser beam, which are adjacent to each other in both horizontal and vertical directions so as to irradiate the entire amorphous silicon thin film on the insulating substrate. However, since the eximer laser beam radiated has a high energy density, crystal grains fuse with each other in the regions where the radiation of the beams overlaps. As a result, the sizes of crystal grains of the polycrystalline silicon thin film vary with each other, and the irregularity of the surface of the polycrystalline silicon thin film increases. Consequently, the characteristics of the thin film transistor such as mobility, ON-voltage and leak current vary significantly from one transistor to another. Thus, such a technique is not suitable for mass production.